Method of preparing and storing GaN substrate, prepared and stored GaN substrate, and semiconductor device and method of its manufacture

ABSTRACT

A GaN substrate storage method of storing, within an atmosphere in which the oxygen concentration is not greater than 15 vol. % and the water-vapor concentration is not greater than 20 g/m 3 , a GaN substrate ( 1 ) having a planar first principal face ( 1   m ), and whose plane orientation in an arbitrary point (P) along the first principal face ( 1   m ) and separated 3 mm or more from the outer edge thereof has an off-inclination angle Δα of −10° or more, 10° or less with respect to the plane orientation of an arbitrarily designated crystalline plane ( 1   a ) that is inclined 50° or more, 90° or less with respect to a plane ( 1   c ), being either the (0001) plane or the (000  1 ) plane, through the arbitrary point. In this way a method of storing GaN substrates whose principal-face plane orientation is other than (0001) or (000  1 ), with which semiconductor devices of favorable properties can be manufactured is made available.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.12/877,086, filed on Sep. 7, 2010 and now U.S. Pat. No. 8,227,826.Application Ser. No. 12/877,086 was a continuation of application Ser.No. 11/762,786, filed on Jun. 14, 2007 and now U.S. Pat. No. 7,811,908.

TECHNICAL FIELD

The present invention relates to methods of storing GaN substrates whoseprincipal-face plane orientation is other than (0001) or (000 1), usedto manufacture semiconductor devices, to such GaN substrates stored bythe storing methods, to semiconductor devices in which an at leastsingle-lamina semiconductor layer is formed onto the GaN substrates, andto methods of manufacturing such semiconductor devices.

BACKGROUND ART

GaN substrates are widely employed in light-emitting diodes (LEDs),laser diodes (LDs) and other semiconductor devices.

In thus employing GaN substrates, the process whereby the substrates aremanufactured is ordinarily separate from the process whereby themanufactured GaN substrates are used to produce semiconductor devices,meaning that the manufactured GaN substrates are stored for a fixed timeperiod, and then used to produce the semiconductor devices. Therefore,various methods of housing and storing manufactured GaN substrates havebeen proposed to date. (For example, cf. Japanese Unexamined Patent App.Pub. 2000-355392).

With these conventional GaN substrate-storing methods, however, inasmuchas the GaN substrates are housed and stored under a clean airatmosphere, the surface of the GaN substrates oxidizes due to theprolonged storage, which has been prohibitive of manufacturingsemiconductor devices with favorable properties.

SUMMARY OF INVENTION Technical Problem

The present invention is directed to solving this problem, and an objectof the invention is to make available: a method of preparing and storingGaN substrates from which semiconductor devices of favorable propertiescan be manufactured, GaN substrates prepared and stored by the method,semiconductor devices in which an at least single-lamina semiconductorlayer is formed on the GaN substrates, and a method of manufacturingsuch semiconductor devices.

Particularly, an object of the present invention, to solve the problemsdiscussed above, is to make available: a method of preparing and storingGaN substrates whose principal-face plane orientation is other than(0001) or (000 1), with which semiconductor devices of favorableproperties such as enabling maintenance of photoemission efficiency at ahigh level, and reduction of blue-shift in the emission from LEDs(light-emitting diodes), LDs (laser diodes) and like semiconductordevices, can be manufactured; such GaN substrates stored and prepared bythe preparing and storing method; semiconductor devices in which an atleast single-lamina semiconductor layer is formed onto the GaNsubstrates; and a method of manufacturing such semiconductor devices.

Solution to Problem

The present invention, in accordance with a certain aspect thereof, is aGaN substrate storage method of storing, within an atmosphere in whichthe oxygen concentration is not greater than 15 vol. % and thewater-vapor concentration is not greater than 20 g/m³, a GaN substratehaving a planar first principal face, and whose plane orientation in anarbitrary point along the first principal face and separated 3 mm ormore from the outer edge thereof has an off-inclination angle of −10° ormore, 10° or less with respect to the plane orientation of anarbitrarily designated crystalline plane that is inclined 50° or more,90° or less with respect to a plane, being either the (0001) plane orthe (000 1) plane, through the arbitrary point.

In a GaN substrate storage method involving the present invention, theoxygen concentration can be made 10 vol. % or less, and the water-vaporconcentration 15 g/m³ or less. Furthermore, the oxygen concentration canbe brought to 6 vol. % or less, and the water-vapor concentration to 5g/m³ or less. Likewise, the atmosphere under which the GaN substratesare stored can be formed from a gaseous mixture containing an inert gas,gaseous oxygen, and water vapor, with the oxygen concentration beingmade not less than 0.05 vol. % and the water-vapor concentration notless than 0.1 g/m³.

Additionally, in a GaN substrate stored by a storing method involvingthe present invention, the average roughness Ra of a first principalface thereof can be made 20 nm or less, while the average roughness Raof a second principal face thereof can be made 20 μm or less.Furthermore, the average roughness Ra of the first principal face can bebrought to 5 nm or less, and the average roughness Ra of the secondprincipal face to 10 μm or less.

And in a GaN substrate stored by a storage method involving the presentinvention, it is possible to have the plane orientation of thearbitrarily designated crystalline plane be {20 2 1}. Therein, the planeorientation in an arbitrary point along the first principal face andseparated 3 mm or more from the outer edge thereof can have anoff-inclination angle of −10° or more, 10° or less in a <1 2 10>direction with respect to {20 2 1}, and of −10° or more, 10° or less ina direction perpendicular to a <20 2 1> direction and to a <1 2 10>direction. Likewise, the plane orientation in an arbitrary point alongthe first principal face and separated 3 mm or more from the outer edgethereof can have an off-inclination angle of −3° or more, 3° or less ina <1 2 10> direction with respect to {20 2 1}, and of −3° or more, 3° orless in a direction perpendicular to a <20 2 1> direction and to a <1 210> direction. Furthermore, the plane orientation in an arbitrary pointalong the first principal face and separated 3 mm or more from the outeredge thereof can have an off-inclination angle of −0.5° or more, 0.5° orless in a <1 2 10> direction with respect to {20 2 1}, and of −0.5° ormore, 0.5° or less in a direction perpendicular to a <20 2 1> directionand to a <1 2 10> direction.

The present invention in accordance with a separate aspect is a GaNsubstrate stored within an atmosphere in which the oxygen concentrationis not greater than 15 vol. % and the water-vapor concentration is notgreater than 20 g/m³, having a planar first principal face, and whoseplane orientation in an arbitrary point along the first principal faceand separated 3 mm or more from the outer edge thereof has anoff-inclination angle of −10° or more, 10° or less with respect to theplane orientation of an arbitrarily designated crystalline plane that isinclined 50° or more, 90° or less with respect to a plane, being eitherthe (0001) plane or the (000 1) plane, through the arbitrary point.

And the present invention in accordance with a still separate aspect isa semiconductor device including an above-described GaN substrate, andan at least single-lamina semiconductor layer formed onto the firstprincipal face of the GaN substrate. The present invention is also asemiconductor device manufacturing method including a step of preparingan above-described GaN substrate, and a step of growing an at leastsingle-lamina semiconductor layer onto the first principal face of theGaN substrate.

Advantageous Effects of Invention

The present invention affords: a method of storing GaN substrates whoseprincipal-face plane orientation is other than (0001) or (000 1), withwhich semiconductor devices of favorable properties can be manufactured;such GaN substrates stored by the storing method; semiconductor devicesin which an at least single-lamina semiconductor layer is formed ontothe GaN substrates; and a method of manufacturing such semiconductordevices.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram representing one mode of embodying a GaNsubstrate storage method involving the present invention.

FIG. 2 is a schematic diagram representing one mode of embodying a GaNsubstrate involving the present invention.

FIG. 3A is a simplified diagram specifically representing one mode ofembodying a GaN substrate involving the present invention to depict asimplified plan view of the GaN substrate.

FIG. 3B is a simplified diagram specifically representing one mode ofembodying a GaN substrate involving the present invention to depict asimplified sectional view along IIIB-IIIB in FIG. 3A.

FIG. 3C is a simplified diagram specifically representing one mode ofembodying a GaN substrate involving the present invention to depict asimplified sectional view along IIIC-IIIC in FIG. 3A.

FIG. 4A is a simplified diagram specifically representing one mode ofembodying a semiconductor device including a GaN substrate involving thepresent invention to depict a simplified plan view of the GaN substrate.

FIG. 4B is a simplified diagram specifically representing one mode ofembodying a semiconductor device including a GaN substrate involving thepresent invention to depict a simplified sectional view along IVB-IVB inFIG. 4A.

FIG. 5 is a simplified sectional diagram representing one mode ofembodying a semiconductor device involving the present invention.

FIG. 6A is a simplified diagram representing a method of manufacturing aGaN substrate involving the present invention to represent an operationof cutting a plurality of GaN parent-crystal pieces from a GaN parentcrystal.

FIG. 6B is a simplified diagram representing a method of manufacturing aGaN substrate involving the present invention to represent an operationof arranging a plurality of GaN parent-crystal pieces adjoining eachother sideways.

FIG. 6C is a simplified diagram representing a method of manufacturing aGaN substrate involving the present invention to represent an operationof growing GaN crystal onto the plurality of parent-crystal GaN piecesand cutting out a GaN substrate.

FIG. 6D is a simplified diagram representing a method of manufacturing aGaN substrate involving the present invention to represent a furtheroperation of growing GaN crystal and cutting out a GaN substrate.

FIG. 7 is a graph charting one example of the relationship betweensemiconductor device properties, and oxygen concentration andwater-vapor concentration in an atmosphere for storing GaN substrates.

FIG. 8 is a graph charting another example of the relationship betweensemiconductor device properties, and oxygen concentration andwater-vapor concentration in an atmosphere for storing GaN substrates.

FIG. 9 is a graph charting a further example of the relationship betweensemiconductor device properties, and oxygen concentration andwater-vapor concentration in an atmosphere for storing GaN substrates.

FIG. 10 is a graph charting a still further example of the relationshipbetween semiconductor device properties, and oxygen concentration andwater-vapor concentration in an atmosphere for storing GaN substrates.

DESCRIPTION OF EMBODIMENTS

In crystallography, in order to express the plane orientation ofcrystalline planes, notation (Miller notation) such as (hkl) or (hkil)is used. The plane orientation of crystalline planes in GroupIII-nitride crystal and other hexagonal-system crystal constituting GaNparent crystal, GaN parent-crystal pieces, GaN crystal, GaN substrates,etc., is expressed by (hkil). Herein, h, k, i and l are integersreferred to as Miller indices, and have the relationship i=−(h+k). Aplane of (hkil) plane orientation is called an (hkil) plane. Likewise,the direction perpendicular to the (hkil) plane (the direction normal tothe (hkil) plane) is called the [hkil] direction. And {hkil} signifies afamily of plane orientations that includes (hkil) and the individualplane orientations that are its crystallographic equivalent, while<hkil> signifies a family of directions that includes [hkil] and theindividual directions that are its crystallographic equivalent.

Embodying Mode 1

Reference is made to FIG. 1 and FIG. 2: One mode of embodying a GaNsubstrate storage method involving the present invention stores, withinan atmosphere in which the oxygen concentration is not greater than 15vol. % and the water-vapor concentration is not greater than 20 g/m³, aGaN substrate 1 having a planar first principal face 1 m, and whoseplane orientation in an arbitrary point P along the first principal face1 m and separated 3 mm or more from the outer edge thereof has anoff-inclination angle (in FIG. 2, off-inclination angle Δα) of −10° ormore, 10° or less with respect to the plane orientation of anarbitrarily designated crystalline plane 1 a that is inclined 50° ormore, 90° or less (in FIG. 2, inclination angle α) with respect to aplane, being either the (0001) plane or the (000 1) plane, through thearbitrary point P.

Storing the aforedescribed GaN substrates under the atmosphere in whichthe oxygen concentration is not greater than 15 vol. % and thewater-vapor concentration is not greater than 20 g/m³ makes it possibleto keep oxidation of the GaN substrate surfaces to a minimum, enablingthe manufacture of semiconductor devices of favorable properties. Fromsuch perspectives, the oxygen concentration is preferably not greaterthan 10 vol. % and the water-vapor concentration not greater than 15g/m³, and more preferably, the oxygen concentration is not greater than6 vol. % and the water-vapor concentration is not greater than 5 g/m³.On the other hand, from the perspective of reducing the cost of creatingthe atmosphere for storing the GaN substrates, preferably the oxygenconcentration is 0.05 vol. % or more and the water-vapor concentrationis 0.1 g/m³ or more.

Herein, the technique whereby in the atmosphere for storing theabove-described GaN substrates the oxygen concentration is made notgreater than 15 vol. % and the water-vapor concentration is made notgreater than 20 g/m³ is not particularly limited, wherein a storingdevice 10 as represented in FIG. 1 may for example be employed. Therein,the storing device 10 in FIG. 1 is equipped with a gas introduction line20, a gas introduction valve 29, a gas exhaust line 40, and a gasexhaust valve 49.

As a way to have the oxygen concentration be no more than 15 vol. % andthe water-vapor concentration be no more than 20 g/m³ in an atmospherefor storing the aforedescribed GaN substrates, one technique (referredto as “Technique I”—likewise below) is, with GaN substrates 1 placedinside the storing device 10, to introduce low gas 23 of oxygenconcentration not greater than 15 vol. % and water-vapor concentrationnot greater than 20 g/m³ into the storing device 10, exhausting gas 43of oxygen concentration higher than 15 vol. % as well as water-vaporconcentration higher than 20 g/m³. Another technique (referred to as“Technique II”—likewise below) is to place, together with the GaNsubstrates 1, an oxygen scavenger 31 and a dehydrating agent 32 a insidethe storing device 10. Moreover, Technique I and Technique II can beemployed in tandem.

Herein, the gas whose oxygen concentration and water-vapor concentrationare, respectively, not greater than 15 vol. % and not greater than 20g/m³ is not particularly limited, but from the perspective of notcausing chemical reactions with the surfaces of the GaN substrates,other than an inert gas such as gaseous nitrogen or gaseous argon,gaseous mixtures containing these inert gases and a predeterminedquantity or less of gaseous oxygen and water vapor are preferable. Inparticular, from a low-cost perspective, a just-mentioned gaseousmixture of an inert gas and gaseous oxygen and water vapor, being agaseous mixture whose oxygen concentration and water-vapor concentrationare, respectively, not greater than 15 vol. % and not greater than 20g/m³, is preferable. Also, the oxygen scavenger is not particularlylimited, but from the perspective of not causing chemical reactions withthe GaN substrate surfaces, active iron oxide, activated carbon, or thelike is preferable. Likewise, while the dehydrating agent is notparticularly limited, from the perspective of not causing chemicalreactions with the GaN substrate surfaces, silica gel, activated carbon,or the like is preferable.

Furthermore, the measuring of the oxygen concentration is notparticularly limited, but can be carried out by means of a galvanicoxygen analyzer. Likewise, the measuring of the water-vaporconcentration is not particularly limited, but may be carried out bymeans of a dielectric aquameter or a Karl Fischer moisture analyzer.

The temperature of the atmosphere for storing the GaN substrates is alsonot particularly limited, but from the perspective of not causingchemical reactions with the surface of the GaN substrates, it ispreferably not greater than 60° C., with not greater than 40° C. beingmore preferable. In addition, from the perspective of preventingcondensation, 5° C. or greater is preferable, with 10° C. or greaterbeing more preferable.

A GaN substrate stored in a storage method of the present embodying modehas, referring to FIG. 2 and FIG. 3, a planar first principal face 1 m,and its plane orientation in an arbitrary point P along the firstprincipal face 1 m and separated 3 mm or more from the outer edgethereof (e.g., Point P_(c), Point P₁, Point P₂, Point P₃, Point P₄,etc.) has an off-inclination angle Δα of −10° or more, 10° or less withrespect to the plane orientation of an arbitrarily designatedcrystalline plane 1 a that is inclined 50° or more, 90° or less (in FIG.2, inclination angle α) with respect to a plane 1 c, being either the(0001) plane or the (000 1) plane, through the arbitrary point P.

With a GaN substrate in the present embodying mode, because (i) it has aplanar first principal face 1 m, and (ii) its plane orientation in anarbitrary point along the first principal face 1 m and separated 3 mm ormore from the outer edge thereof has an off-inclination angle Δα of −10°or more, 10° or less with respect to the plane orientation of anarbitrarily designated crystalline plane 1 a that is inclined 50° ormore, 90° or less with respect to a plane 1 c, being either the (0001)plane or the (000 1) plane, through the arbitrary point, by growing anat least single-lamina semiconductor layer onto the first principal face1 m, a semiconductor device of minimal blue shift in photoemission andhigh emission efficiency is obtained. In particular, because theoff-inclination angle Δα of its plane orientation in an arbitrary pointalong the first principal face 1 m and separated 3 mm or more from theouter edge thereof is small, in the aforedescribed storing of the GaNsubstrate, inside the storing device reacting of oxygen and water vaporwith the surfaces of the GaN substrate is controlled to a minimum, andthe amount of oxygen and water-vapor adsorption onto the GaN substratesurfaces is reduced, whereby high-emission-efficiency semiconductordevices is obtained.

Furthermore, as for GaN substrates of the present embodying mode, fromthe perspectives of keeping reaction of oxygen and water vapor insidethe storing device with the GaN substrate surfaces under control, and ofreducing the amount of oxygen and water-vapor adsorption into the GaNsubstrate surfaces, preferably the average roughness Ra of the firstprincipal face 1 m is not greater than 20 nm, and the average roughnessRa of the second principal face 1 n is not greater than 20 μm. From suchperspectives, it is more preferable that the average roughness Ra of thefirst principal face 1 m be 5 nm or less, and that the average roughnessRa of the second principal face 1 n be 10 μm or less. Although therelationship between the average roughness Ra of first principal face 1m and second principal face 1 n of the GaN substrate 1 and thereactivity and adsorptivity of oxygen and water vapor with theseprincipal faces 1 m and 1 n of the GaN substrate 1 is not clear, thereduction in surface area from lessening the average roughness Ra isbelieved to be relevant as one causative factor. Herein, the “firstprincipal face 1 m” means the principal face on which semiconductorlayers are grown, while the “second principal face 1 n” means theprincipal face on the side opposite from said first principal face 1 m.Furthermore, “average roughness Ra of a surface” means arithmetic meanroughness Ra stipulated in JIS B 0601:2001, and refers to a value inwhich a predetermined reference surface area is chosen from theroughness topography along its average plane, and the absolute values ofthe deviation from the average plane of the chosen portion to theprofiling topography are summed and the total is averaged in thereference surface area. Such surface average roughness Ra can bemeasured employing a non-contact interferometer, 3D-SEM(three-dimensional scanning electron micrometer), AFM (atomic-forcemicroscope), or the like.

With further regard to a GaN substrate of the present embodying mode,referring to FIG. 2, the plane orientation of the foregoing arbitrarilydesignated crystalline plane 1 a preferably is {20 2 1}. With a GaNsubstrate 1 in which the plane orientation in an arbitrary point P alongthe first principal face 1 m of the GaN substrate 1 and separated 3 mmor more from the outer edge thereof has an off-inclination angle Δα of−10° or more, 10° or less with respect to {20 2 1} because semiconductorlayers of high crystalline quality can be grown stably onto its firstprincipal face 1 m, a semiconductor device of minimal blue shift inphotoemission and high emission efficiency is obtained.

Further in respect of a GaN substrate of the present embodying mode,referring to FIG. 2 and FIG. 3, from the perspectives of keeping oxygenand water vapor inside the storing device from reacting with the GaNsubstrate surfaces, and of reducing the amount of oxygen and water-vaporadsorption into the GaN substrate surfaces, preferably the planeorientation in an arbitrary point P along the first principal face 1 mand separated 3 mm or more from the outer edge thereof (e.g., PointP_(c), Point P₁, Point P₂, Point P₃ and Point P₄) has an off-inclinationangle Δα of −10° or more, 10° or less in a <1 2 10> direction, and of−10° or more, 10° or less in a direction perpendicular to a <20 2 1>direction and to a <1 2 10> direction, more preferably has anoff-inclination angle Δα of −3° or more, 3° or less in a <1 2 10>direction with respect to {20 2 1}, and of −3° or more, 3° or less in adirection perpendicular to a <20 2 1> direction and to a <1 2 10>direction, and still more preferably has an off-inclination angle of−0.5° or more, 0.5° or less in a <1 2 10> direction with respect to {202 1}, and of −0.5° or more, 0.5° or less in a direction perpendicular toa <20 2 1> direction and to a <1 2 10> direction.

While the relationship between the off-inclination angle Δα between {202 1} and the plane orientation in an arbitrary point along the firstprincipal face 1 m of the GaN substrate 1 and separated 3 mm or morefrom the outer edge thereof, and the reactivity and adsorptivity ofoxygen and water vapor with respect to the first principal face 1 m ofthe GaN substrate 1 is not clear, what is believed to be relevant as onecausative factor is that having a predetermined off-inclination angle Δαvaries the number of sites along the first principal face 1 m of the GaNsubstrate 1 where oxygen and water vapor may bond. The off-inclinationangle Δα between {20 2 1} and the plane orientation in an arbitrarypoint along the first principal face of the GaN substrate and separated3 mm or more from the outer edge thereof can be measured by an XRD(x-ray diffraction) technique.

Here, in the present embodying mode, referring to FIG. 1, with theatmosphere inside the storing device 10 in which the GaN substrates 1are housed having been rendered storing conditions in the invention ofthe present application (for example, that the oxygen concentration benot greater than 15 vol. % and the water-vapor concentration be notgreater than 20 g/m³), the GaN substrates 1 can be stored by sealing theGaN substrates 1 into a (not-illustrated) storage container (e.g., analuminum pouch or the like) that shuts out oxygen and water vapor.Further, GaN substrates hermetically sealed in a storage container canbe taken out of the storing device 10 and stored.

With reference to FIG. 6, in a GaN substrate manufacturing method of thepresent embodying mode, while not particularly limited, included are: astep (FIG. 6A) of cutting from a GaN parent crystal 100 a plurality ofGaN parent-crystal pieces 100 p and 100 q having principal faces 100 pmand 100 qm whose off-inclination angle is −5° or more, 5° or less withrespect to a plane orientation {hkil} having an inclination angle α of50° or more, 90° or less with respect to a plane, being either the(0001) plane or the (000 1) plane, of the GaN parent crystal; a step(FIG. 6B) of arranging the GaN parent-crystal pieces 100 p and 100 qadjoining each other sideways in such a way that the principal faces 100pm and 100 qm of the GaN parent-crystal pieces 100 p and 100 q paralleleach other, and the [0001] directions of the GaN parent-crystal pieces100 p and 100 q are identical; a step (FIG. 6C) of growing GaN crystal110 onto the principal faces 100 pm and 100 qm of the GaN parent-crystalpieces 100 p and 100 q; and a step (FIG. 6C) of cutting out a GaNsubstrate 1 of Embodying Mode 1 from the grown GaN crystal 110.

In the above-described steps, GaN crystal 110 in which the off-anglebetween the plane orientation of the principal face of a sectionalregion 110 p of the GaN crystal 110 that grows onto the GaNparent-crystal piece 100 p, and the plane orientation of the principalface of a sectional region 110 q of the GaN crystal 110 that grows ontothe GaN parent-crystal piece 100 q is −10° or more, 10° or less can begrown. Herein, the sectional regions 110 p and 110 q of the GaN crystal110 are regions of the GaN crystal partitioned by planes (referred to asextension planes 110 t hereinafter) extending, into the GaN crystal 110interior, the lateral sides 100 pt and 100 qt where the GaNparent-crystal pieces 100 p and 100 q adjoin each other.

By cutting the thus-obtained GaN crystal 110 in planes 110 u and 110 vparallel to the plane of the {hkil} plane orientation mentioned earlier,a GaN substrate 1 having a planar first principal face 1 m, and whoseplane orientation in an arbitrary point along the first principal face 1m and separated 3 mm or more from the outer edge thereof has anoff-inclination angle of −10° or more, 10° or less with respect to theplane orientation of an arbitrarily designated crystalline plane that isinclined 50° or more, 90° or less with respect to a plane, being eitherthe (0001) plane or the (000 1) plane, through the arbitrary point isobtained.

Therein, from the perspective of making the off-inclination anglethrough the aforementioned arbitrary point in the GaN substrate 1 small,the off-inclination angle with respect to the aforementioned planeorientation {hkil} of the principal faces 100 pm and 100 qm of theplurality of GaN parent-crystal pieces 100 p and 100 q preferably is−10° or more, 10° or less, more preferably −3° or more, 3° or less,still more preferably −0.5° or more, 0.5° or less. And from theperspective of growing GaN crystal of high crystalline quality, theaverage roughness Ra of the principal faces 100 pm and 100 qm andlateral sides 100 pt and 100 qt of the GaN parent-crystal pieces 100 pand 100 q preferably is not greater than 50 nm, more preferably notgreater than 5 nm.

And the method for growing the GaN crystal 110, while not particularlylimited preferably is, from the perspective of growing GaN crystal ofhigh crystalline quality, a vapor-phase method such as an HVPE (hydridevapor-phase epitaxy) technique, an MOCVD (metalorganic chemical vapordeposition) technique or an MBE (molecular-beam epitaxy) technique, or aliquid-phase method such as flux growth. From the perspective of thecrystal growth rate being considerable, an HVPE technique is furtherpreferable. If the GaN crystal 110 is grown by an HVPE technique, fromthe perspective of making the off-inclination angle through theaforementioned arbitrary point in the GaN substrate 1 small, thecrystal-growth conditions preferably are that the crystal-growthtemperature is 950° C. or more, 1200° C. or less, and the crystal-growthrate is 30 μm/hr or more, 300 μm/hr or less.

In a method of manufacturing a GaN substrate of the present embodyingmode, a step (FIG. 6D) of utilizing, as a GaN starting substrate 110 s,a GaN substrate 1 cut out from the grown GaN crystal 110 in planes 110 uand 110 v parallel to a plane of {hkil} plane orientation, and growingfurther GaN crystal 120 onto the principal face 110 pm of such GaNstarting substrate 110 s, and a step (FIG. 6D) of cutting a GaNsubstrate 1 of Embodying Mode 1 out from the grown further GaN crystal120 can further be included.

By the above-described steps, further GaN crystal 120 in which theoff-angle between the plane orientation of the principal face of asectional region 120 p of the further GaN crystal 120 that grows ontothe sectional region 110 p of the GaN starting substrate 110 s, and theplane orientation of the principal face of a sectional region 120 q ofthe further GaN crystal 120 that grows onto the sectional region 110 qof the GaN starting substrate 110 s is −10° or more, 10° or less can begrown. Herein, the sectional regions 120 p and 120 q of the further GaNcrystal 120 are regions of the further GaN crystal partitioned by planes(referred to as extension planes 120 t hereinafter) extending, into thefurther GaN crystal 120 interior, the extension planes 110 t of the GaNstarting substrate 110 s.

By cutting the thus-obtained further GaN crystal 120 in planes 120 u and120 v parallel to the plane of {hkil} plane orientation, a GaN substrate1 having a planar first principal face 1 m, and whose plane orientationin an arbitrary point along the first principal face 1 m and separated 3mm or more from the outer edge thereof has an off-inclination angle of−10° or more, 10° or less with respect to the plane orientation of anarbitrarily designated crystalline plane that is inclined 50° or more,90° or less with respect to a plane, being either the (0001) plane orthe (000 1) plane, through the arbitrary point is obtained.

The method for growing the further GaN crystal 120, while notparticularly limited preferably is, from the perspective of growing GaNcrystal of high crystalline quality, a vapor-phase method such as anHVPE technique, an MOCVD technique or an MBE technique, or aliquid-phase method such as flux growth. From the perspective of thecrystal growth rate being considerable, an HVPE technique is furtherpreferable. If the further GaN crystal 120 is grown by an HVPEtechnique, from the perspective of making the off-inclination anglethrough the aforementioned arbitrary point in the GaN substrate 1 small,the crystal-growth conditions preferably are that the crystal-growthtemperature is 950° C. or more, 1200° C. or less, and the crystal-growthrate is 30 μm/hr or more, 300 μm/hr or less.

Embodying Mode 2

Reference is made to FIG. 1 through FIG. 3: One mode of embodying a GaNsubstrate involving the present invention is a GaN substrate 1, storedwithin an atmosphere in which the oxygen concentration is not greaterthan 15 vol. % and the water-vapor concentration is not greater than 20g/m³, having a planar first principal face 1 m, and whose planeorientation in an arbitrary point along the first principal face 1 m andseparated 3 mm or more from the outer edge thereof has anoff-inclination angle Δα of −10° or more, 10° or less with respect tothe plane orientation of an arbitrarily designated crystalline plane 1 athat is inclined 50° or more, 90° or less with respect to a plane 1 c,being either the (0001) plane or the (000 1) plane, through thearbitrary point. With a GaN substrate of the present embodying mode,stored by a method of Embodying Mode 1, because surface oxidation iskept to a minimum, by growing an at least single-lamina semiconductorlayer onto the first principal face 1 m, a semiconductor device ofsuperior properties is obtained.

Embodying Mode 3

Reference is made to FIG. 4 and FIG. 5: One mode of embodying asemiconductor device involving the present invention includes a GaNsubstrate 1 of Embodying Mode 2, stored by a method of Embodying Mode 1,and an at least single-lamina semiconductor layer 210 formed onto thefirst principal face 1 m of the GaN substrate 1. With a semiconductordevice of the present embodying mode, because a semiconductor layer 210of high crystalline quality is formed onto the first principal face 1 mof a GaN substrate 1 in which oxidation of its surfaces has been kept toa minimum, a semiconductor device of superior properties is obtained.

There are no particular limitations on the semiconductor layer 210formed onto the GaN substrate 1, but in view of the crystal latticesbeing highly coordinate, a Group III nitride semiconductor layer such asan Al_(x)Ga_(y)In_(1-x-y)N (0≦x, 0≦y, x+y≦1) layer is preferable.Likewise, while there are no particular limitations on thesemiconductor-layer formation method, from the perspective of forming asemiconductor layer 210 of high crystalline quality onto the GaNsubstrate 1, it is preferable to employ an HVPE technique, an MOCVDtechnique or an MBE technique. From the viewpoint of allowing precisecontrol of the thickness and chemical composition of the semiconductorlayer 210 formed onto the GaN substrate 1, an MOCVD technique is furtherpreferable.

With a semiconductor device of the present embodying mode, referring toFIG. 4 and FIG. 5, specifically an n-type GaN lamina 211, anIn_(0.2)Ga_(0.8)N lamina 212, an Al_(0.2)Ga_(0.8)N lamina 213, and ap-type GaN lamina 214 are formed as the at least single-laminasemiconductor layer 210 in order onto the first principal face 1 m of aGaN substrate 1 of Embodying Mode 2, and further, onto the secondprincipal face 1 n of the GaN substrate 1, an n-side electrode 221 isformed, and onto the principal face of the p-type GaN layer 214 a p-sideelectrode 222 is, wherein photoemission 230 is put out.

Embodiment 4

Reference is made to FIG. 3 through FIG. 5: One mode of embodying amethod, involving the present invention, of manufacturing asemiconductor device includes a step of preparing a GaN substrate 1 ofEmbodying Mode 2, stored by a method of Embodying Mode 1, and a step ofgrowing an at least single-lamina semiconductor layer 210 onto the firstprincipal face 1 m of the GaN substrate 1. By such steps a semiconductordevice of superior properties is obtained.

A semiconductor-device manufacturing method of the present embodyingmode, referring to FIG. 3 through FIG. 5, includes the step of preparinga GaN substrate 1 of Embodying Mode 2, stored by a method of EmbodyingMode 1. Such step of preparing a GaN substrate 1 is as set forth inEmbodying Mode 1 and Embodying Mode 2.

A semiconductor-device manufacturing method of the present embodyingmode, referring to FIG. 4 and FIG. 5, includes the step of growing an atleast single-lamina semiconductor layer 210 onto the first principalface 1 m of the GaN substrate 1. The semiconductor layer 210 grown ontothe GaN substrate 1, while not particularly limited, preferably is, inview of the crystal lattices being highly coordinate, a Group IIInitride semiconductor layer such as an Al_(x)Ga_(y)In_(1-x-y)N (0≦x,0≦y, x+y≦1) layer. Likewise, while there are no particular limitationson the semiconductor-layer growth method, from the perspective ofepitaxially growing the semiconductor layer 210 with ease onto the GaNsubstrate 1, it is preferable to employ an HVPE technique, an MOCVDtechnique or an MBE technique. From the viewpoint of allowing precisecontrol of the thickness and chemical composition of the semiconductorlayer 210 grown onto the GaN substrate 1, an MOCVD technique is furtherpreferable.

With a semiconductor device manufacturing method of the presentembodying mode, referring to FIG. 4 and FIG. 5, by for example growing,by means of an MOCVD technique, in order onto the first principal face 1m of the GaN substrate 1 of Embodying Mode 2, an n-type GaN lamina 211,an In_(0.2)Ga_(0.8)N lamina 212, an Al_(0.2)Ga_(0.8)N lamina 213, and ap-type GaN lamina 214, as the at least single-lamina semiconductor layer210, a semiconductor layer wafer 200 u is obtained. Subsequently, byforming an n-side electrode 221 onto the second principal face 1 n ofthe GaN substrate 1 in the semiconductor layer wafer 200 u, and forminga p-side electrode 222 onto the principal face of the p-type GaN layer214, a semiconductor device 200 is obtained. The thus-obtainedsemiconductor device 200 puts out photoemission 230.

EMBODIMENT EXAMPLES Embodiment Example I

1. Manufacture of GaN Substrates

Reference is made to FIG. 6A: The (0001) side and the (000 1) side—thetwo principal faces—of a GaN parent crystal 100 of 50.8 mm diameter and3 mm thickness, produced by an HVPE technique, were ground and polishedto an average roughness Ra of the two principal faces of 5 nm. Herein,the average roughness Ra of the surfaces was characterized employingAFM.

Subsequently, the GaN parent crystal 100 with the average roughness Raof its two principal faces having been made 5 nm was sliced in aplurality of planes perpendicular to <20 1 1> directions, whereby aplurality of GaN parent-crystal pieces 100 p and 100 q, having {20 2 1}principal faces, of 3.1 mm width, 20 to 50.8 mm length, and 1 mmthickness were cut from it. Following that, the not-ground andnot-polished four sides of each cut-out GaN parent-crystal piece wereground and polished to bring the average roughness Ra of the four sidesto 5 nm. Thus, a plurality of GaN parent-crystal pieces whose {20 2 1}principal-face average roughness Ra was 5 nm were obtained. Among theseGaN parent-crystal pieces were GaN parent-crystal pieces whoseprincipal-face plane orientation did not coincide with {20 2 1}, buteven with any of such GaN parent-crystal pieces the off-inclinationangle of its principal-face plane orientation with respect to {20 2 1}was −0.1° or more, 0.4° or less. Herein, the off-inclination angle wasmeasured by x-ray diffractometry.

Next, referring to FIG. 6B, these GaN parent-crystal pieces werearranged adjoining each other sideways inside the crystal-growth chamberof an HVPE apparatus, in such a way that the {20 2 1} principal faces100 pm and 100 qm of the plurality of GaN parent-crystal pieces 100 pand 100 q paralleled each other, and in such a way that the [0001]directions of the GaN parent-crystal pieces 100 p and 100 q wereidentical. In that situation, referring to FIG. 1C, the averageroughness Ra of the mutually adjoining lateral sides 100 pt and 100 qtof the plurality of GaN parent-crystal pieces 100 p and 100 q was 5 nm.The diameter of a circle inscribed on the outer periphery of, as whole,the plurality of GaN parent-crystal pieces 100 p and 100 q arranged inthis way was 50.8 mm.

Next, referring to FIG. 6C, the {20 2 1} principal faces 100 pm and 100qm of the plurality of GaN parent-crystal pieces 100 p and 100 qarranged inside the crystal-growth chamber of the HVPE apparatus weretreated two hours at 800° C. under a mixed-gas atmosphere of 10 vol. %gaseous hydrogen chloride (HCl) and 90 vol. % gaseous nitrogen (N₂),after which GaN crystal 110 was grown 50 hours by an HVPE technique ontothe principal faces 100 pm and 100 qm under conditions in which thepartial pressure of the hydrogen chloride gas that reacts with the Gamelt to generate the Ga chloride gas that is the Ga source-material gaswas 2.2 kPa, the partial pressure of the ammonia (NH₃) gas that is thenitrogen source-material gas was 15.6 kPa, and the crystal-growthtemperature was 1080° C.

The thickness of the obtained GaN crystal 110 was measured by a contactthickness gauge (a “Digimatic Indicator,” Mitutoyo Corp. mfr.),whereupon it was 4 mm. That meant that the crystal growth rate was 80μm/hr. Referring to FIG. 6C, FIG. 2 and FIG. 3: By cutting eight GaNsubstrates out of this GaN crystal 110 in planes 110 u and 110 vparallel to a {20 2 1} plane, and carrying out grinding and polishingprocesses on their two principal faces, eight GaN substrates wereobtained, of 50.8 mm diameter×400 μm thickness, whose firstprincipal-face 1 m average roughness Ra was 3 nm and whose secondprincipal-face 1 n average roughness Ra was 8 μm, and whoseoff-inclination angle toward a <1 2 10> direction (the x-axis directionin FIG. 3) and whose off-inclination angle toward a direction (they-axis direction in FIG. 3) perpendicular to a <20 2 1> direction and a<1 2 10> direction—being the off-inclination angles between the firstprincipal face and a {20 2 1} plane in each of points, along the firstprincipal face 1 m, Point P_(c), Point P₁, Point P₂, Point P₃ and PointP₄—are each entered in Table I.

Herein, referring to FIG. 3, Point P_(c), is a point in the middle ofthe GaN substrate 1 on its first principal face 1 m, while Point P₁,Point P₂, Point P₃ and Point P₄ are each a point on the first principalface and separated 3 mm from the outer edge thereof, with Point P₁,Point P_(c) and Point P₂ lying in that order on a straight line in a <12 10> direction and Point P₃, Point P_(c) and Point P₄ lying in thatorder on a straight line in a direction perpendicular to a <20 2 1>direction and a <1 2 10> direction.

2. Storing of GaN Substrates

Each of seven GaN substrates within the eight GaN substrates obtained asabove-described was washed and then stored for six months within anatmosphere having the oxygen concentrations and water-vaporconcentrations set forth in Table I—within atmospheres being a gaseousmixture of gaseous nitrogen as an inert gas, gaseous oxygen, and watervapor (Ex. I-1 through Ex. I-6 and Ex. I-R1). The remaining single GaNsubstrate, without undergoing storage of this sort, after theaforementioned production and washing of the GaN substrate was within 10minutes placed inside the crystal-growth reaction chamber of an MOCVDapparatus, and semiconductor devices were fabricated as in the following(Ex. I-S).

3. Fabrication of Semiconductor Devices

Referring to FIG. 4 and FIG. 5: The foregoing seven GaN substratesfollowing storage (Ex. I-1 through Ex. I-6 and Ex. I-R1) and thenon-stored single GaN substrate (Ex. I-S) were each placed inside thecrystal-growth reaction chamber of an MOCVD apparatus, and a 5-μm thickn-type GaN lamina 211, a 3-nm thick In_(0.2)Ga_(0.8)N lamina 212, a60-nm thick Al_(0.2)Ga_(0.8)N lamina 213, and a 150-nm thick p-type GaNlamina 214 were grown in order, as the semiconductor layer 210, onto thefirst principal face 1 m of each GaN substrate 1 to yield asemiconductor wafer 200 u. Herein, Point Q_(c), Point Q₁, Point Q₂,Point Q₃ and Point Q₄ on the principal face of the semiconductor layer210 in the semiconductor wafer 200 u are each positioned on a linenormal to its first principal face through the Point P_(c), Point P₁,Point P₂, Point P₃ and Point P₄ on the first principal face 1 m of theGaN substrate 1.

As indicated in FIG. 4, in four neighbor regions of Point Q₁, Point Q₂,Point Q₃ and Point Q₄ of 5 mm width, separated 3 mm to 10 mm from theouter edge of the principal face of the semiconductor wafer 200 u, a100-nm thick p-side electrode 222 was formed onto the principal face ofthe p-type GaN lamina 214, and then an 80-μm diameter×100-nm thickn-side electrode 221 was formed onto the second principal face of theGaN substrate, to yield, as semiconductor devices 200, ten in eachneighbor region for a total 40 LEDs of 500 μm×500 μm geometry. Thephotoemission intensity of the 40 LEDs obtained in this way was measuredby means of a spectral photometer, and their average photoemissionintensities were computed. The relative average photoemissionintensities of Ex. I-S, Ex. I-1 through Ex. I-6 and Ex. I-R1, lettingthe average photoemission intensity of semiconductor device Ex. I-S be1.00, were tabulated in Table I.

TABLE I Embodiment Example I Ex. I-S Ex. I-1 Ex. I-2 Ex. I-3 Ex. I-4 Ex.I-5 Ex. I-6 Ex. I-R1 GaN Substrate diameter (mm) 50 50 50 50 50 50 50 50substrate Off-inclination Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.20.2 0.2 0.2 angle of P_(c) Direct. perpend. 0.1 0.1 0.1 0.1 0.1 0.1 0.10.1 pricipal face to <20 2 1> (^(o)) direct. and <1 2 10> direct. Point<1 2 10> direction 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 P₁ Direct prepend.0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10> direct.Point <1 2 10> direction −0.1 −0.1 −0.1 −0.1 −0.1 −0.1 −0.1 −0.1 P₂Direct. perpend. 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and<1 2 10> direct. Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 P₃ Direct. perpend. 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 to <20 2 1>direct. and <1 2 10> direct. Point <1 2 10> direction 0.2 0.2 0.2 0.20.2 0.2 0.2 0.2 P₄ Direct. perpend. −0.3 −0.3 −0.3 −0.3 −0.3 −0.3 −0.3−0.3 to <20 2 1> direct. and <1 2 10> direct. Substrate Oxygen conc. —15 15 0.05 10 6 0.05 18 storage (vol. %) conditions Water-vapor — 20 0.120 15 5 0.1 25 conc. (g/m³) Temperature (° C.) — 25 25 25 25 25 25 25Storage term (mo.) — 6 6 6 6 6 6 6 Semicon. Device type LED LED LED LEDLED LED LED LED device Relative Photoemission intensity 1.00 0.75 0.880.78 0.85 0.96 1.00 0.47 (referent)

Referring to Table I, with regard to semiconductor devices in which anat least single-lamina semiconductor layer was formed onto the firstprincipal face of a GaN substrate whose plane orientation in anarbitrary point (e.g., Point P₁, Point P₂, Point P₃ or Point P₄) alongthe first principal face and separated 3 mm or more from the outer edgethereof had an off-inclination angle of −0.5° or more, 0.5° or less in a<1 2 10> direction with respect to {20 2 1} and −0.5° or more, 0.5° orless in a direction perpendicular to a <20 2 1> direction and a <1 2 10>direction, the following was understood. The relative averagephotoemission intensity of semiconductor devices (Ex. I-1 through Ex.I-6) utilizing GaN substrates stored within an atmosphere ranging froman oxygen concentration of 0.05 vol. % and water-vapor concentration of0.1 g/m³ to an oxygen concentration of 15 vol. % and water-vaporconcentration of 20 g/m³ was sustained at a high 0.75 to 1.00 withrespect to the relative average photoemission intensity of thesemiconductor device (Ex. I-S) employing the post-formation not-storedGaN substrate.

Embodiment Example II

1. Manufacture of GaN Substrates

In the same way as with Embodiment Example I, a plurality of GaNparent-crystal pieces was cut from a GaN parent crystal. With any of thecut-out GaN parent-crystal pieces, the off-inclination angle of itsprincipal-face plane orientation with respect to {20 2 1} was −2° ormore, 2° or less. Next, the plurality of GaN parent crystals wasarranged in the same way as with Embodiment Example I, and GaN crystalwas grown by an HVPE technique onto their principal face. The GaNcrystal was grown 40 hours under conditions in which the partialpressure of the hydrogen chloride gas that reacts with the Ga melt togenerate the Ga chloride gas that is the Ga source-material gas was 3.3kPa, the partial pressure of the ammonia (NH₃) gas that is the nitrogensource-material gas was 15.6 kPa, and the crystal-growth temperature was1080° C. The obtained GaN crystal had 5 mm thickness. That meant thatthe crystal growth rate was 125 μm/hr. Next, in the same way as withEmbodiment Example I, by cutting eight GaN substrates out of the GaNcrystal and grinding and polishing their two principal faces, eight GaNsubstrates were obtained, of 50.8 mm diameter×400 μm thickness, whosefirst principal-face average roughness Ra was 4.3 nm and whose secondprincipal-face average roughness Ra was 9.3 μm, and whoseoff-inclination angle toward a <1 2 10> direction and whoseoff-inclination angle toward a direction perpendicular to a <20 2 1>direction and a <1 2 10> direction—being the off-inclination anglesbetween the first principal face and a {20 2 1} plane in each of points,along the first principal face, Point P_(c), Point P₁, Point P₂, PointP₃ and Point P₄—are each entered in Table II.

2. Storing of GaN Substrates

Each of seven GaN substrates within the eight GaN substrates obtained asabove-described was washed and then stored for six months within anatmosphere having the oxygen concentrations and water-vaporconcentrations set forth in Table II—within atmospheres being a gaseousmixture of gaseous nitrogen as an inert gas, gaseous oxygen, and watervapor (Ex. II-1 through Ex. II-6 and Ex. II-R1). The remaining singleGaN substrate, without undergoing storage of this sort, after theaforementioned production and washing of the GaN substrate was within 10minutes placed inside the crystal-growth reaction chamber of an MOCVDapparatus, and semiconductor devices were fabricated as in the following(Ex. II-S).

3. Fabrication of Semiconductor Devices

On each of the foregoing seven GaN substrates following storage (Ex.II-1 through Ex. II-6 and Ex. II-R1) and the non-stored single GaNsubstrate (Ex. II-S), in the same way as with Embodiment Example I, 40LEDs, being semiconductor devices, were fabricated. The relative averagephotoemission intensities of Ex. II-1 through Ex. II-6 and Ex. II-R1,letting the average photoemission intensity of semiconductor device Ex.II-S be 1.00, were tabulated in Table II.

TABLE II Embodiment Example II Ex. II-S Ex. II-1 Ex. II-2 Ex. II-3 Ex.II-4 GaN Substrate diameter (mm) 50 50 50 50 50 substrateOff-inclination Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 angle ofP_(c) Direct. perpend. 0.1 0.1 0.1 0.1 0.1 pricipal face to <20 2 1>(^(o)) direct. and <1 2 10> direct. Point <1 2 10> direction 2.8 2.8 2.82.8 2.8 P₁ Direct prepend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and<1 2 10> direct. Point <1 2 10> direction −2.5 −2.5 −2.5 −2.5 −2.5 P₂Direct. perpend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10>direct. Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 P₃ Direct. perpend.2.7 2.7 2.7 2.7 2.7 to <20 2 1> direct. and <1 2 10> direct. Point <1 210> direction 0.2 0.2 0.2 0.2 0.2 P₄ Direct. perpend. −2.5 −2.5 −2.5−2.5 −2.5 to <20 2 1> direct. and <1 2 10> direct. Substrate Oxygenconc. — 15 15 0.05 10 storage (vol. %) conditions Water-vapor — 20 0.120 15 conc. (g/m³) Temperature (° C.) — 25 25 25 25 Storage term (mo.) —6 6 6 6 Semicon. Device type LED LED LED LED LED device RelativePhotoemission intensity 1.00 0.66 0.83 0.75 0.8 (referent) EmbodimentExample II Ex. II-5 Ex. II-6 Ex. II-R1 GaN Substrate diameter (mm) 50 5050 substrate Off-inclination Point <1 2 10> direction 0.2 0.2 0.2 angleof P_(c) Direct. perpend. 0.1 0.1 0.1 pricipal face to <20 2 1> (^(o))direct. and <1 2 10> direct. Point <1 2 10> direction 2.8 2.8 2.8 P₁Direct prepend. 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10> direct.Point <1 2 10> direction −2.5 −2.5 −2.5 P₂ Direct. perpend. 0.1 0.1 0.1to <20 2 1> direct. and <1 2 10> direct. Point <1 2 10> direction 0.20.2 0.2 P₃ Direct. perpend. 2.7 2.7 2.7 to <20 2 1> direct. and <1 2 10>direct. Point <1 2 10> direction 0.2 0.2 0.2 P₄ Direct. perpend. −2.5−2.5 −2.5 to <20 2 1> direct. and <1 2 10> direct. Substrate Oxygenconc. 6 0.05 18 storage (vol. %) conditions Water-vapor 5 0.1 25 conc.(g/m³) Temperature (° C.) 25 25 25 Storage term (mo.) 6 6 6 Semicon.Device type LED LED LED device Relative Photoemission intensity 0.920.97 0.43

Referring to Table II, with regard to semiconductor devices in which anat least single-lamina semiconductor layer was formed onto the firstprincipal face of a GaN substrate whose plane orientation in anarbitrary point (e.g., Point P₁, Point P₂, Point P₃ or Point P₄) alongthe first principal face and separated 3 mm or more from the outer edgethereof had an off-inclination angle of −3.0° or more, 3.0° or less in a<1 2 10> direction with respect to {20 2 1} and −3.0° or more, 3.0° orless in a direction perpendicular to a <20 2 1> direction and a <1 2 10>direction, the following was understood. The relative averagephotoemission intensity of semiconductor devices (Ex. II-1 through Ex.II-6) utilizing GaN substrates stored within an atmosphere ranging froman oxygen concentration of 0.05 vol. % and water-vapor concentration of0.1 g/m³ to an oxygen concentration of 15 vol. % and water-vaporconcentration of 20 g/m³ was sustained at a high 0.66 to 0.97 withrespect to the relative average photoemission intensity of thesemiconductor device (Ex. II-S) employing the post-formation not-storedGaN substrate.

Embodiment Example III

1. Manufacture of GaN Substrates

In the same way as with Embodiment Example I, a plurality of GaNparent-crystal pieces was cut from a GaN parent crystal. With any of thecut-out GaN parent-crystal pieces, the off-inclination angle of itsprincipal-face plane orientation with respect to {20 2 1} was −5° ormore, 5° or less. Next, the plurality of GaN parent crystals wasarranged in the same way as with Embodiment Example I, and GaN crystalwas grown by an HVPE technique onto their principal face. The GaNcrystal was grown 40 hours under conditions in which the partialpressure of the hydrogen chloride gas that reacts with the Ga melt togenerate the Ga chloride gas that is the Ga source-material gas was 4.3kPa, the partial pressure of the ammonia (NH₃) gas that is the nitrogensource-material gas was 15.6 kPa, and the crystal-growth temperature was1080° C. The obtained GaN crystal had 6 mm thickness. That meant thatthe crystal growth rate was 150 μm/hr. Next, in the same way as withEmbodiment Example I, by cutting eight GaN substrates out of the GaNcrystal and grinding and polishing their two principal faces, eight GaNsubstrates were obtained, of 50.8 mm diameter×400 μm thickness, whosefirst principal-face average roughness Ra was 2.3 nm and whose secondprincipal-face average roughness Ra was 3.1 μm, and whoseoff-inclination angle toward a <1 2 10> direction and whoseoff-inclination angle toward a direction perpendicular to a <20 2 1>direction and a <1 2 10> direction—being the off-inclination anglesbetween the first principal face and a {20 2 1} plane in each of points,along the first principal face, Point P_(c), Point P₁, Point P₂, PointP₃ and Point P₄—are each entered in Table III.

2. Storing of GaN Substrates

Each of seven GaN substrates within the eight GaN substrates obtained asabove-described was washed and then stored for six months within anatmosphere having the oxygen concentrations and water-vaporconcentrations set forth in Table III—within atmospheres being a gaseousmixture of gaseous nitrogen as an inert gas, gaseous oxygen, and watervapor (Ex. III-1 through Ex. III-6 and Ex. III-R1). The remaining singleGaN substrate, without undergoing storage of this sort, after theaforementioned production and washing of the GaN substrate was within 10minutes placed inside the crystal-growth reaction chamber of an MOCVDapparatus, and semiconductor devices were fabricated as in the following(Ex. III-S).

3. Fabrication of Semiconductor Devices

On each of the foregoing seven GaN substrates following storage (Ex.III-1 through Ex. III-6 and Ex. III-R1) and the non-stored single GaNsubstrate (Ex. III-S), in the same way as with Embodiment Example I, 40LEDs, being semiconductor devices, were fabricated. The relative averagephotoemission intensities of Ex. III-1 through Ex. III-6 and Ex. III-R1,letting the average photoemission intensity of semiconductor device Ex.III-S be 1.00, were tabulated in Table III.

TABLE III Embodiment Example III Ex. III-S Ex. III-1 Ex. III-2 Ex. III-3Ex. III-4 GaN Substrate diameter (mm) 50 50 50 50 50 substrateOff-inclination Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 angle ofP_(c) Direct. perpend. 0.1 0.1 0.1 0.1 0.1 pricipal face to <20 2 1>(^(o)) direct. and <1 2 10> direct. Point <1 2 10> direction 6 6 6 6 6P₁ Direct prepend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10>direct. Point <1 2 10> direction −5.8 −5.8 −5.8 −5.8 −5.8 P₂ Direct.perpend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10> direct.Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 P₃ Direct. perpend. −5.5−5.5 −5.5 −5.5 −5.5 to <20 2 1> direct. and <1 2 10> direct. Point <1 210> direction 0.2 0.2 0.2 0.2 0.2 P₄ Direct. perpend. 5.6 5.6 5.6 5.65.6 to <20 2 1> direct. and <1 2 10> direct. Substrate Oxygen conc. — 1515 0.05 10 storage (vol. %) conditions Water-vapor — 20 0.1 20 15 conc.(g/m³) Temperature (° C.) — 25 25 25 25 Storage term (mo.) — 6 6 6 6Semicon. Device type LED LED LED LED LED device Relative Photoemissionintensity 1.00 0.59 0.77 0.70 0.75 (referent) Embodiment Example III Ex.III-5 Ex. III-6 Ex. III-R1 GaN Substrate diameter (mm) 50 50 50substrate Off-inclination Point <1 2 10> direction 0.2 0.2 0.2 angle ofP_(c) Direct. perpend. 0.1 0.1 0.1 pricipal face to <20 2 1> (^(o))direct. and , <1 2 10> direct. Point <1 2 10> direction 6 6 6 P₁ Directprepend. 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10> direct. Point <1 210> direction −5.8 −5.8 −5.8 P₂ Direct. perpend. 0.1 0.1 0.1 to <20 2 1>direct. and <1 2 10> direct. Point <1 2 10> direction 0.2 0.2 0.2 P₃Direct. perpend. −5.5 −5.5 −5.5 to <20 2 1> direct. and <1 2 10> direct.Point <1 2 10> direction 0.2 0.2 0.2 P₄ Direct. perpend. 5.6 5.6 5.6 to<20 2 1> direct. and <1 2 10> direct. Substrate Oxygen conc. 6 0.05 18storage (vol. %) conditions Water-vapor 5 0.1 25 conc. (g/m³)Temperature (° C.) 25 25 25 Storage term (mo.) 6 6 6 Semicon. Devicetype LED LED LED device Relative Photoemission intensity 0.90 0.95 0.37

Referring to Table III, with regard to semiconductor devices in which anat least single-lamina semiconductor layer was formed onto the firstprincipal face of a GaN substrate whose plane orientation in anarbitrary point (e.g., Point P₁, Point P₂, Point P₃ or Point P₄) alongthe first principal face and separated 3 mm or more from the outer edgethereof had an off-inclination angle of −6.0° or more, 6.0° or less in a<1 2 10> direction with respect to {20 2 1} and −6.0° or more, 6.0° orless in a direction perpendicular to a <20 2 1> direction and a <1 2 10>direction, the following was understood. The relative averagephotoemission intensity of semiconductor devices (Ex. III-1 through Ex.III-6) utilizing GaN substrates stored within an atmosphere ranging froman oxygen concentration of 0.05 vol. % and water-vapor concentration of0.1 g/m³ to an oxygen concentration of 15 vol. % and water-vaporconcentration of 20 g/m³ was sustained at a high 0.59 to 0.95 withrespect to the relative average photoemission intensity of thesemiconductor device (Ex. III-S) employing the post-formation not-storedGaN substrate.

Embodiment Example IV

1. Manufacture of GaN Substrates

In the same way as with Embodiment Example I, a plurality of GaNparent-crystal pieces was cut from a GaN parent crystal. With any of thecut-out GaN parent-crystal pieces, the off-inclination angle of itsprincipal-face plane orientation with respect to {20 2 1} was −9° ormore, 9° or less. Next, the plurality of GaN parent crystals wasarranged in the same way as with Embodiment Example I, and GaN crystalwas grown by an HVPE technique onto their principal face. The GaNcrystal was grown 40 hours under conditions in which the partialpressure of the hydrogen chloride gas that reacts with the Ga melt togenerate the Ga chloride gas that is the Ga source-material gas was 6.4kPa, the partial pressure of the ammonia (NH₃) gas that is the nitrogensource-material gas was 15.6 kPa, and the crystal-growth temperature was1080° C. The obtained GaN crystal had 8 mm thickness. That meant thatthe crystal growth rate was 200 μm/hr. Next, in the same way as withEmbodiment Example I, by cutting eight GaN substrates out of the GaNcrystal and grinding and polishing their two principal faces, eight GaNsubstrates were obtained, of 50.8 mm diameter×400 μm thickness, whosefirst principal-face average roughness Ra was 0.6 nm and whose secondprincipal-face average roughness Ra was 0.8 μm, and whoseoff-inclination angle toward a <1 2 10> direction and whoseoff-inclination angle toward a direction perpendicular to a <20 2 1>direction and a <1 2 10> direction—being the off-inclination anglesbetween the first principal face and a {20 2 1} plane in each of points,along the first principal face, Point P_(c), Point P₁, Point P₂, PointP₃ and Point P₄—are each entered in Table IV.

2. Storing of GaN Substrates

Each of seven GaN substrates within the eight GaN substrates obtained asabove-described was washed and then stored for six months within anatmosphere having the oxygen concentrations and water-vaporconcentrations set forth in Table IV—within atmospheres being a gaseousmixture of gaseous nitrogen as an inert gas, gaseous oxygen, and watervapor (Ex. IV-1 through Ex. IV-6 and Ex. IV-R1). The remaining singleGaN substrate, without undergoing storage of this sort, after theaforementioned production and washing of the GaN substrate was within 10minutes placed inside the crystal-growth reaction chamber of an MOCVDapparatus, and semiconductor devices were fabricated as in the following(Ex. IV-S).

3. Fabrication of Semiconductor Devices

On each of the foregoing seven GaN substrates following storage (Ex.IV-1 through Ex. IV-6 and Ex. IV-R1) and the non-stored single GaNsubstrate (Ex. IV-S), in the same way as with Embodiment Example I, 40LEDs, being semiconductor devices, were fabricated. The relative averagephotoemission intensities of Ex. IV-1 through Ex. IV-6 and Ex. IV-R1,letting the average photoemission intensity of semiconductor device Ex.IV-S be 1.00, were tabulated in Table IV.

TABLE IV Embodiment Example IV Ex. IV-S Ex. IV-1 Ex. IV-2 Ex. IV-3 Ex.IV-4 GaN Substrate diameter (mm) 50 50 50 50 50 substrateOff-inclination Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 angle ofP_(c) Direct. perpend. 0.1 0.1 0.1 0.1 0.1 pricipal face to <20 2 1>(^(o)) direct. and <1 2 10> direct. Point <1 2 10> direction 9.7 9.7 9.79.7 9.7 P₁ Direct prepend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and<1 2 10> direct. Point <1 2 10> direction −9.8 −9.8 −9.8 −9.8 −9.8 P₂Direct. perpend. 0.1 0.1 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10>direct. Point <1 2 10> direction 0.2 0.2 0.2 0.2 0.2 P₃ Direct. perpend.−9.5 −9.5 −9.5 −9.5 −9.5 to <20 2 1> direct. and <1 2 10> direct. Point<1 2 10> direction 0.2 0.2 0.2 0.2 0.2 P₄ Direct. perpend. 9.6 9.6 9.69.6 9.6 to <20 2 1> direct. and <1 2 10> direct. Substrate Oxygen conc.— 15 15 0.05 10 storage (vol. %) conditions Water-vapor — 20 0.1 20 15conc. (g/m³) Temperature (° C.) — 25 25 25 25 Storage term (mo.) — 6 6 66 Semicon. Device type LED LED LED LED LED device Relative Photoemissionintensity 1.00 0.51 0.65 0.60 0.64 (referent) Embodiment Example IV Ex.IV-5 Ex. IV-6 Ex. IV-R1 GaN Substrate diameter (mm) 50 50 50 substrateOff-inclination Point <1 2 10> direction 0.2 0.2 0.2 angle of P_(c)Direct. perpend. 0.1 0.1 0.1 pricipal face to <20 2 1> (^(o)) direct.and , <1 2 10> direct. Point <1 2 10> direction 9.7 9.7 9.7 P₁ Directprepend. 0.1 0.1 0.1 to <20 2 1> direct. and <1 2 10> direct. Point <1 210> direction −9.8 −9.8 −9.8 P₂ Direct. perpend. 0.1 0.1 0.1 to <20 2 1>direct. and <1 2 10> direct. Point <1 2 10> direction 0.2 0.2 0.2 P₃Direct. perpend. −9.5 −9.5 −9.5 to <20 2 1> direct. and <1 2 10> direct.Point <1 2 10> direction 0.2 0.2 0.2 P₄ Direct. perpend. 9.6 9.6 9.6 to<20 2 1> direct. and <1 2 10> direct. Substrate Oxygen conc. 6 0.05 18storage (vol. %) conditions Water-vapor 5 0.1 25 conc. (g/m³)Temperature (° C.) 25 25 25 Storage term (mo.) 6 6 6 Semicon. Devicetype LED LED LED device Relative Photoemission intensity 0.80 0.90 0.31

Referring to Table IV, with regard to semiconductor devices in which anat least single-lamina semiconductor layer was formed onto the firstprincipal face of a GaN substrate whose plane orientation in anarbitrary point (e.g., Point P₁, Point P₂, Point P₃ or Point P₄) alongthe first principal face and separated 3 mm or more from the outer edgethereof had an off-inclination angle of −10.0° or more, 10.0° or less ina <1 2 10> direction with respect to {20 2 1} and −10.0° or more, 10.0°or less in a direction perpendicular to a <20 2 1> direction and a <1 210> direction, the following was understood. The relative averagephotoemission intensity of semiconductor devices (Ex. IV-1 through Ex.IV-6) utilizing GaN substrates stored within an atmosphere ranging froman oxygen concentration of 0.05 vol. % and water-vapor concentration of0.1 g/m³ to an oxygen concentration of 15 vol. % and water-vaporconcentration of 20 g/m³ was sustained at a high 0.51 to 0.90 withrespect to the relative average photoemission intensity of thesemiconductor device (Ex. IV-S) employing the post-formation not-storedGaN substrate.

It should be noted that although in the foregoing Embodiment Example Ithrough Embodiment Example IV the storing term is in each case 6 months,it has been verified that the effects obtained do not change if thestoring term is under 6 months or exceeds 6 months.

The embodying modes and embodiment examples disclosed at this timeshould in all respects be considered to be illustrative and notlimiting. The scope of the present invention is set forth not by theforegoing description but by the scope of the claims, and is intended toinclude meanings equivalent to the scope of the claims and allmodifications within the scope.

REFERENCE SIGNS LIST

1: GaN substrate; 1 a: crystalline plane; 1 c: plane being either the(0001) plane or the (000 1) plane; 1 m, 1 n, 100 pm, 100 qm, 110 pm:principal faces; 10: storing device; 20: gas introduction line; 23, 43:gases; 29: gas introduction valve; 31: oxygen scavenger; 32: dehydratingagent; 40: gas exhaust line; 49: gas exhaust valve; 100: GaN parentcrystal; 100 p, 100 q: GaN parent-crystal pieces; 100 pt, 100 qt:lateral sides; 110, 120: GaN crystal; 110 p, 110 q, 120 p, 120 q:sectional regions; 110 s: GaN starting substrate; 110 t, 120 t:extension planes; 110 u, 110 v, 120 u, 120 v: parallel planes; 200:semiconductor device; 200 u: semiconductor wafer; 210: semiconductorlayer; 211: n-type GaN lamina; 212: In_(0.2)Ga_(0.8)N lamina; 213:Al_(0.2)Ga_(0.8)N lamina; 214: p-type GaN lamina; 221: n-side electrode;222: p-side electrode; 230: photoemission

The invention claimed is:
 1. A GaN substrate preparation and storagemethod comprising: a substrate-preparation step of preparing a GaNsubstrate, defining first and second principal faces as distinct fromthe substrate edge, so as to have a planar first principal face and aplane orientation, in an arbitrary point along the first principal faceand separated 3 mm or more from the outer edge thereof, having anoff-inclination angle of between −10° and 10°, inclusive, with respectto the plane orientation of an arbitrarily designated crystalline planethat is inclined between 50° and 90°, inclusive, with respect to aplane, being either the (0001) plane or the (000 1) plane, through thearbitrary point; a storage-atmosphere preparation step of preparing aGaN-substrate storage atmosphere of not greater than 15 vol. % oxygenconcentration and not greater than 20 g/m³ water-vapor concentration;and a storage step of storing the prepared GaN substrate within theatmosphere prepared in said storage-atmosphere preparation step.
 2. TheGaN substrate preparation and storage method set forth in claim 1,wherein in said storage-atmosphere preparation step, the atmosphere isprepared to have an oxygen concentration of not greater than 10 vol. %and a water-vapor concentration of not greater than 15 g/m³.
 3. The GaNsubstrate preparation and storage method set forth in claim 1, whereinin said storage-atmosphere preparation step, the atmosphere is preparedto have an oxygen concentration of not greater than 6 vol. % and awater-vapor concentration of not greater than 5 g/m³.
 4. The GaNsubstrate preparation and storage method set forth in claim 1, whereinin said storage-atmosphere preparation step, the atmosphere is preparedby forming the atmosphere from a gaseous mixture containing an inertgas, gaseous oxygen, and water vapor, and such that the oxygenconcentration is not less than 0.05 vol. % and the water-vaporconcentration is not less than 0.1 g/m³.
 5. The GaN substratepreparation and storage method set forth in claim 1, wherein insubstrate-preparation step, the GaN substrate is prepared so as to havea first-principal-face average roughness Ra of 20 nm or less, and asecond-principal-face average roughness Ra of 20 μm or less.
 6. The GaNsubstrate preparation and storage method set forth in claim 1, whereinin substrate-preparation step, the GaN substrate is prepared so as tohave a first-principal-face average roughness Ra of 5 nm or less, and asecond-principal-face average roughness Ra of 10 μm or less.
 7. The GaNsubstrate preparation and storage method set forth in claim 1, whereinin said substrate-preparation step the plane orientation of thearbitrarily designated crystalline plane, with respect to which thefirst-principal-face arbitrary-point plane orientation of the GaNsubstrate is made to be off-angled, is {20 2 1}.
 8. The GaN substratepreparation and storage method set forth in claim 7, wherein in saidsubstrate-preparation step the first-principal-face arbitrary-pointplane orientation of the GaN substrate is made to be off-angled between−10° and 10°, inclusive, in a <1 2 10> direction with respect to {20 21}, and between −10° and 10°, inclusive, in a direction perpendicular toa <20 2 1> direction and to a <1 2 10> direction.
 9. The GaN substratepreparation and storage method set forth in claim 7, wherein in saidsubstrate-preparation step the first-principal-face arbitrary-pointplane orientation of the GaN substrate is made to be off-angled between−3° and 3°, inclusive, in a <1 2 10> direction with respect to {20 2 1},and between −3° and 3°, inclusive, in a direction perpendicular to a <202 1> direction and to a <1 2 10> direction.
 10. The GaN substratepreparation and storage method set forth in claim 7, wherein in saidsubstrate-preparation step the first-principal-face arbitrary-pointplane orientation of the GaN substrate is made to be off-angled between−0.5° and 0.5°, inclusive, in a <1 2 10> direction with respect to {20 21}, and between −0.5° and 0.5°, inclusive, in a direction perpendicularto a <20 2 1> direction and to a <1 2 10> direction.
 11. A GaN substratestored within an atmosphere in which the oxygen concentration is notgreater than 15 vol. % and the water-vapor concentration is not greaterthan 20 g/m³, having a planar first principal face, and whose planeorientation in an arbitrary point along the first principal face andseparated 3 mm or more from the outer edge thereof has anoff-inclination angle of between −10° and 10°, inclusive, with respectto the plane orientation of an arbitrarily designated crystalline planethat is inclined between 50° and 90°, inclusive, with respect to aplane, being either the (0001) plane or the (000 1) plane, through thearbitrary point.
 12. A semiconductor device including a GaN substrate ofclaim 11, and an at least single-lamina semiconductor layer formed ontothe first principal face of the GaN substrate.
 13. A semiconductordevice manufacturing method comprising: a step of obtaining a GaNsubstrate prepared and stored according to the method of claim 1; and astep of growing an at least single-lamina semiconductor layer onto thefirst principal face of the GaN substrate.